Orifice Sizing

What is the fluid, its temperature and pressure?

PWSlack,

Fluid is warer at around 90°C & 2.0 kg/cm2 pressure.

If you assume that the flow will be same then you have a proportionality as follows:

Δp= k*(Q/A)^2 where Q=flow and A= orifice area. For a circular orifice the relationship becomes Δp=k*( Q/d^2)^2 so that if you write it for 2 pressure drops you get:

Δp1= k*(Q/d1^2)^2 and Δp2=k*(Q/d2^2)^2 the ratio of the equations leads to

d2/d1= (Δp1 / Δp2)^(1/4)

This is only an indication since the changes in the area has also effects on the k value which is quite complex so that the best is to make the new diameter a bit smaller than the computed value and make a trial and if necessary the correction by enlarging it.

Thnaks nick for Guidance. As you said assumption needs to be kept in mind.

If flow has to be modified then you use same equation and introduce as well flows as diameters. For simplicity I considered that at least maximal flow is the same.

Anyway principle is the same and as long as fluid viscosity is not modified in an important manner so that the Reynolds number stays in same domain nature of fluid and pressure have no influence on result. Fluid temperature can change viscosity more than pressure in most cases.

Nick's formula is fine, but I'm puzzled by the figures.

From flow and pipe data given I calculate ΔP 682 kPa. To give 80 kPa I get orifice dia. 67.8 mm. Can you confirm data?

Cheers.........Codey

Hi CDM,

I counter-checked the data and come to following results:

with 80kPa, d=40mm and water the flow should be 563 to 592 l/min !

With specified flow of 1730 l/min pressure drop should to be 755 to 834 kPa !

I have the feeling that the value was a factor 10 too low for what ever reason it was written 80 kPa instead of 800kPa. The last value being almost the mean of the 2 values (min and max) I obtained = 0.5*(755+834)=794.5 kPa. I considered for the flow global coefficient values from 0.59 to 0.62. The value used usually is 0.6...0.61 and the mean is 0.605!

So you are right something does not fit together.

Usually I limit my intervention to the question and try to answer to it as compact and as professional as possible and I do not care about data since those are responsibility of the one who gives them.

Due to your comment I was tempted, this time, to check and although we do not come to same results (which is normal and to be expected) the trend is the same.

Regards

Nick

Experiment with the hole size and measure your pressures. It sounds like you are measuring delta P. Install and Use a manual valve and simply adjust your delta p where you want it by moving the valve handle open or closed. This give you operating flexibility. and would appear to meet your objective. Are round holes necessary?

Install a variable orifice; these things are called "valves".